linux-kernel - Re: 3.1.0-rc3 -- INFO: possible circular locking dependency detected

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Message-ID: <CA+5PVA7fHAsSGFo4hcTtegT8a4K3xk=XTNYC7GzSYDbgRKc1ug@mail.gmail.com>
Date:	Tue, 23 Aug 2011 09:32:28 -0400
From:	Josh Boyer <jwboyer@...il.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	Miles Lane <miles.lane@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: 3.1.0-rc3 -- INFO: possible circular locking dependency detected

On Tue, Aug 23, 2011 at 9:04 AM, Dave Chinner <david@...morbit.com> wrote:
> On Tue, Aug 23, 2011 at 07:59:20AM -0400, Josh Boyer wrote:
>> On Tue, Aug 23, 2011 at 7:49 AM, Dave Chinner <david@...morbit.com> wrote:
>> >> >  Possible unsafe locking scenario:
>> >> >
>> >> >       CPU0                    CPU1
>> >> >       ----                    ----
>> >> >  lock(&mm->mmap_sem);
>> >> >                               lock(&sb->s_type->i_mutex_key);
>> >> >                               lock(&mm->mmap_sem);
>> >> >  lock(&sb->s_type->i_mutex_key);
>> >> >
>> >> >  *** DEADLOCK ***
>> >>
>> >> This one was reported yesterday: https://lkml.org/lkml/2011/8/21/163
>> >> and we're hoping Ted (or someone else from the ext4 camp) can comment
>> >> on why ext4_evict_inode is holding i_mutex.
>> >
>> > Actually, the problem has nothing to do with ext4. the problem is
>> > that remove_vma() is holding the mmap_sem while calling fput(). The
>> > correct locking order is i_mutex->mmap_sem, as documented in
>> > mm/filemap.c:
>> >
>> >  *  ->i_mutex                   (generic_file_buffered_write)
>> >  *    ->mmap_sem                (fault_in_pages_readable->do_page_fault)
>> >
>> >
>> > The way remove_vma() calls fput() also triggers lockdep reports in
>> > XFS and it will do so with any filesystem that takes an inode
>> > specific lock in it's evict() processing. IOWs, remove_vma() needs
>> > fixing, not ext4....
>>
>> Er... ok.  So the remove_vma code hasn't changed since 2008.  We're
>> only seeing this issue now because the debugging code has improved,
>> or?
>
> The problem has been there since at least 2008.  Here's an early
> XFS report from 2.6.24:
>
> http://oss.sgi.com/archives/xfs/2008-02/msg00931.html
>
> Here's an XFS report
> to match the ext4 one in this thread from 2009:
>
> http://oss.sgi.com/archives/xfs/2009-03/msg00149.html
>
> You won't find reports much older than this - it only started to be
> reported when lockdep support in XFS matured and it started to be
> widely used....
>
>> At any rate, the proposed solution is to make remove_vma drop mmap_sem
>> before calling fput, or make it not call fput, or?
>
> Ask the VM folk - this is the only response I can remember from them
> is this:
>
> http://oss.sgi.com/archives/xfs/2009-03/msg00224.html
>
> Maybe now that ext4 is hitting the problem something will be done
> about it...

OK.  I've CC'd Andrew and Hugh, so maybe we can get a discussion going.

josh
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